laser equipment in which pumping every dependence of output beam diameter and beam wavefront curvature is reduced. The total pumping energy of at least one of laser active media disposed beyond terminal laser beam waists, among beam waists, is approximately one-half of the total pumping energy of laser active media disposed between two adjacent beam waists.
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3. A method of exciting laser equipment including a plurality of laser active media, each laser active medium generating a lens effect in response to excitation, the plurality of laser active media being arranged in series in a region along a beam axis of the laser equipment and forming a plurality of beam waists in a laser beam within the region, the method comprising:
applying a first pumping energy to a first of the laser active media, the first of the laser active media being disposed beyond at least one of the beam waists, at an end of the region, to produce a first thermal-lens focal length, and
applying a second pumping energy to a second of the laser active media, the second of the laser active media being disposed between two adjacent beam waists, to produce a second thermal-lens focal length, wherein the first thermal-lens focal length is approximately twice as long as the second thennal-lens focal length.
2. A method of exciting laser equipment including a plurality of laser active media, each laser active medium generating a lens effect in response to excitation, the plurality of laser active media being arranged in series in a region along a beam axis of the laser equipment and forming a plurality of beam waists in a laser beam within the region, the method comprising:
applying a first pumping energy to a first of the laser active media, the first of the laser active media being disposed beyond at least one of the beam waists, at an end of the region, and
applying a second pumping energy to a second of the laser active media, the second of the laser active media being disposed between two adjacent beam waists, wherein
the second pumping energy is larger than the first pumping energy,
both of the first and second of the laser active media have end faces and are configured for being excited on their end faces,
the first of the laser active media is pumped though only one end face, and
the second of the laser active media is pumped though both end faces.
6. A method of exciting laser equipment that includes a plurality of doped laser active media in the form of rods and having the same dopant concentration, each laser active medium generating a lens effect in response to excitation, the plurality of laser active media being arranged in series in a region along a beam axis of the laser equipment and forming a single beam waist in a laser beam within the region, the method comprising:
applying a first pumping energy to a first of the laser active media, the first of the laser active media being disposed flanking the beam waist on a first side,
applying a second pumping energy to a second of the laser active media, the second of the laser active media being disposed flanking the beam waist on a second side, wherein
the first pumping energy is approximately one-half of the second pumping energy,
the first and second of the laser active media include respective first and second excitation portions having respective first and second excitation lengths, and the first and second excitation lengths are the same, and
the first and second of the laser active media have equal diameters.
4. A method of exciting laser equipment that includes a plurality of doped laser active media in the form of rods and having the same dopant concentration, each laser active medium generating a lens effect in response to excitation, the plurality of laser active media being arranged in series in a region along a beam axis of the laser equipment and forming a single beam waist in a laser beam within the region, the method comprising:
applying a first pumping energy to a first of the laser active media, the first of the laser active media being disposed flanking the beam waist on a first side,
applying a second pumping energy to a second of the laser active media, the second of the laser active media being disposed flanking the beam waist on a second side, wherein
the first pumping energy is approximately one-half of the second pumping energy,
the first and second of the laser active media include respective first and second excitation portions having respective first and second excitation lengths, and the first excitation length is one-half of the second excitation length, and
the first and second of the laser active media have equal diameters.
5. A method of exciting laser equipment that includes a plurality of doped laser active media in the form of rods and having the same dopant concentration, each laser active medium generating a lens effect in response to excitation, the plurality of laser active media being arranged in series in a region along a beam axis of the laser equipment and forming a plurality of beam waists in a laser beam within the region, the method comprising:
applying a first pumping energy to a first of the laser active media, the first of the laser active media being disposed beyond at least one of the beam waists, at an end of the region, and
applying a second pumping energy to a second of the laser active media, the second of the laser active media being disposed between two adjacent beam waists, wherein
the first pumping energy is approximately one-half the second pumping energy,
the first and second of the laser active media have respective first and second excitation portions having respective first and second excitation lengths, and the first excitation length equals the second excitation length; and
the first and second of the laser active media have equal diameters.
1. A method of exciting laser equipment that includes a plurality of doped laser active media in the form of rods and having the same dopant concentration, each laser active medium generating a lens effect in response to excitation, the plurality of laser active media being arranged in series in a region along a beam axis of the laser equipment and forming a plurality of beam waists in a laser beam within the region, the method comprising:
applying a first pumping energy to a fast of the laser active media, the first of the laser active media being disposed beyond at least one of the beam waists, at an end of the region, and
applying a second pumping energy to a second of the laser active media, the second of the laser active media being disposed between two adjacent beam waists, wherein
the first pumping energy is approximately one-half the second pumping energy,
the first and second of the laser active media have respective first and second excitation portions having respective first and second excitation lengths, and the first excitation length is one-half the second excitation length; and
the first and second of the laser active media have equal diameters.
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The present invention relates to diminishing of variation in laser beam parameters that depend on changes in pumping energy, in laser equipment and laser machining devices that include laser active media, the optical properties of which change depending on changes in the pumping energy.
In
Moreover, 60a, 60b, 60c and 60d are reference marks indicating optical systems that include thermal lenses formed by the laser active media that are situated respectively between 111a and 111b, 111b and 111c, 111c and 111d, and 111d and 111e. A plurality of optical elements that are arranged along the laser beam axis is referred to as an optical system hereinafter, when it is shown as a whole.
The operation of the conventional example illustrated in
The laser equipment constituted as shown in
In a conventional cascade-type solid-state laser oscillator and amplifier as described above, the diameter of the beam in places in which the wavelength-conversion active media are positioned varies depending on the pumping intensity, and the condition of the wavelength conversion accordingly changes depending on the pumping intensity when wavelength conversion using the extracted beam is carried out, since emitted laser beam diameter and beam wavefront curvature varies significantly depending on the pumping intensity. Moreover, when a laser beam generated in the conventional laser equipment is guided into an optical fiber, the light-guiding conditions depends largely on the laser pumping intensity, since the diameter of the emitted beam and the wavefront curvature varies significantly depending on the pumping intensity. In addition, when a laser beam extracted from the conventional laser equipment is used for machining work, the processing conditions varies depending on the pumping intensity of the laser equipment, e.g., laser beam energy, since emitted beam varies depending on the pumping intensity.
On the other hand, assuming for example that the amplifier portion consisting of the laser pumping sections 5c and 5d shown in
The present invention has been made to address the foregoing problems of the conventional laser equipment; it is an object of the present invention to provide laser equipment wherein the beam diameter of an emitted laser beam and the wavefront curvature have reduced dependence on the pumping intensity, as well as laser equipment that can efficiently amplify an incident beam having fixed beam parameters.
According to the present invention, there is provided laser equipment constituted in such a way that a plurality of laser active media each generating a lens effect under excitation are arranged in series along the laser beam axis, and a plurality of beam waists are formed in the laser beam within the region where the plurality of laser active media are arranged, wherein pumping energy for one or more of the laser active media being disposed endwise beyond at least one of the beam waists at either end of the plurality of beam waists is smaller than pumping energy for one or more of the laser active media arranged between two adjacent beam waists among the plurality of beam waists.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of an emitted beam that depends on change in the pumping energy is small, or wherein an incident beam that remains identical over a wide range of variation in the pumping energy can propagate with its cascade-like beam mode being mostly unchanged; therefore, significantly efficient amplification is enabled.
Moreover, there is provided laser equipment wherein pumping energy for one or more of laser active media being disposed endwise beyond at least one of beam waists at either end of the plurality of beam waists, is made from 25% to 75% of the pumping energy for one or more of laser active media arranged between two adjacent beam waists among the plurality of beam waists.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is small, as well as wherein an incident beam that remains identical over a wide range of variation in the pumping energy can propagate further with its cascade-like beam mode being mostly unchanged, and significantly efficient amplification is enabled.
Furthermore, there is provided laser equipment wherein energy for one or more of the laser active media being disposed endwise beyond at least one of the beam waists at either end of the plurality of beam waists is approximately half of the pumping energy for one or more of laser active media arranged between two adjacent beam waists among the plurality of beam waists.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is substantially small, as well as wherein an incident beam that remains identical over a wide range of variation in the pumping energy can propagate with hardly any modification to the cascade-like beam mode, and significantly efficient amplification is enabled.
In addition, there is provided laser equipment wherein the laser active media are constituted to be pumped through their end faces, and the laser active medium arranged at the end beyond at least one of the beam waists that are situated in each end position of the plurality of beam waists is pumped through only one end face, whereas one or more of laser active media arranged between two adjacent beam waists among the plurality of beam waists is pumped through both of its end faces.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of an emitted beam is substantially small, as well as wherein an incident beam that remains identical over a wide range of variation in the pumping energy can propagate with hardly any modification to the cascade-like beam mode, and significantly efficient amplification is enabled.
Moreover, there is provided laser equipment wherein the laser active media are rod-type solid-state laser active media.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is substantially small, as well as wherein the effect, of an incident beam that remains identical over a wide range of variation in the pumping energy being able to propagate with hardly any modification to the cascade-like beam mode, is more largely demonstrated.
Furthermore, there is provided laser equipment wherein 90-degree polarization-direction rotators are arranged along the laser beam axis.
According to the invention, laser equipment can be provided wherein difference in beam parameters that depend on the polarization direction is small, and variation in beam wavefront curvature and in beam diameter of the emitted beam is small.
Moreover, there is provided laser equipment wherein the laser beam outputted from the laser equipment is converted in wavelength.
According to the invention, wavelength-conversion-type laser equipment that is operable over a wide range of pumping energy can be provided, wherein variation in wavelength-conversion conditions, and in beam wavefront curvature and in beam diameter of a wavelength-converted beam is small.
Furthermore, there is provided laser equipment wherein the laser beam outputted from the laser equipment is guided into an optical fiber.
According to the invention, laser equipment can be provided wherein the output beam can stably be extracted from an optical fiber regardless of change in pumping energy.
Moreover, there is provided laser equipment wherein the thermal-lens focal length of one or more of laser active media arranged at the end beyond at least one of beam waists that are situated in each end position of a plurality of beam waists is made approximately twice as long as the thermal-lens focal length of one or more of laser active media arranged between two adjacent beam waists among the plurality of beam waists.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is substantially small, as well as wherein an incident beam that remains identical over a wide range of variation in pumping energy can propagate with hardly any modification to the cascade-like beam mode; therefore, significantly efficient amplification is enabled.
Still furthermore, there is provided laser equipment wherein a plurality of laser active media that generates a lens effect under excitation is arranged in series on the laser beam axis, and a single beam waist is formed in the laser beam within a region where the plurality of laser active media is arranged, and wherein pumping energy for one or more of laser active media arranged on one of the sides that sandwich the beam waist is made approximately half of the pumping energy for one or more of laser active media arranged on the other side.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is substantially small, as well as wherein an incident beam that remains identical over a wide range of variation in the pumping energy can propagate with hardly any modification to the cascade-like beam mode; therefore, significantly efficient amplification is enabled.
Moreover, there is provided laser equipment wherein in a laser resonator that includes between a totally reflecting mirror and a partially reflecting mirror a plurality of laser active media that generates a lens effect under excitation, a beam waist is included; and pumping energy for one or more of laser active media arranged between the beam waist and the totally reflecting mirror is made approximately the same as pumping energy for one or more of laser active media arranged between the beam waist and the partially reflecting mirror.
According to the invention, laser equipment can be provided wherein damage to optical elements does not readily occur, and variation in beam wavefront curvature and in beam diameter of the emitted beam is small.
Still moreover, there is provided laser equipment wherein a plurality of laser active media each generating a lens effect under excitation are arranged in series along a laser beam axis so as to enable a laser beam to propagate in a cyclic propagation shape, wherein the laser beam is made to enter or to be emitted through the vicinity of collimating points in the cyclic propagation shape.
According to the invention, laser equipment can be provided wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is small even when pumping energy is changed, as well as wherein an incident beam that remains identical over a wide range of variation in the pumping energy can propagate with its cascade-like beam mode being mostly unchanged; therefore, significantly efficient amplification is enabled.
In addition, there is provided a laser machining device according to the present invention, wherein the laser equipment is used as a beam source.
According to the invention, laser equipment is made available wherein machining work can stably be carried out regardless of change in the output power.
Furthermore, there is provided a laser-equipment pumping method according to the present invention. In the laser equipment constituted in such a way that a plurality of laser active media that generates a lens effect under excitation is arranged in series along the laser beam axis, and that a plurality of beam waists is formed in the laser beam within the region where the plurality of laser active media is arranged, the laser-equipment pumping method is implemented to excite the laser equipment in such a way that pumping energy for one or more of the laser active media being disposed endwise beyond at least one of the beam waists at either end of the plurality of beam waists is made approximately half of the pumping energy for one or more of the laser active media arranged between two adjacent beam waists among the plurality of beam waists.
According to the invention, laser equipment can be implemented wherein variation in beam wavefront curvature and in beam diameter of the emitted beam is substantially small, as well as wherein an incident beam that remains identical over a wide range of variation in pumping energy can propagate with hardly any modification to the cascade-like beam mode; therefore significantly efficient amplification is enabled.
Three laser pumping sections 5a, 5b and 5c are constituted identical to each other, that is to say, in such a manner that the laser active media 4a, 4b and 4c are identical to each other in specifications such as size, shape and Nd-atom doping concentration, and that the laser-active-medium pumping devices 3a, 3b and 3c are also constituted identical to each other, that is, in the pumping energy, the pumping energy density and the pumping beam absorption properties of the laser active media. Moreover, the total energy that excites the laser active medium 40a arranged in the laser pumping section 50a is half of the total pumping energy of each of the laser active media 4a, 4b and 4c arranged in the pumping sections 5a, 5b and 5c; the length of the excited portion of the laser active medium 40a is half of the length of the excited portion of each of the other laser active media 4a, 4b and 4c. In other words, in the laser active medium 40a, the portion that is half of the laser active media 4a, 4b and 4c in length is excited by the same pumping energy density as are the laser active media 4a, 4b and 4c.
The constitution of laser equipment according to Embodiment 1 is now described in detail. In
Since the laser pumping section 50a is constituted in such a way that the pumping energy is half of that of any one of the laser pumping sections 5a, 5b and 5c, and the length of the excited region of the laser active medium 40a is half of that of any one of the other laser active media 4a, 4b and 4c, when the laser active medium 40a is excited, the optical properties along the laser beam axis of the optical system that ranges from the position 111d to the emitting end 100 of the laser active medium 40a are equivalent to the optical system 6a. In other words, since the pumping energy of the laser active medium 40a arranged at the end beyond the beam waist 111d, which is in the endmost position among the beam waists, is half of that of the laser active medium 4c situated between adjacent beam waists 111c and 111d and is half of that of the laser active media 4a and 4b located between the other adjacent beam waists, the focal length of the thermal lens formed by the laser active medium 40a is twice as long.
Referring to the overall structure described above, it is constituted in such a way that the optical systems are arranged in the order 6a, 6b, 6a, 6b, 6a, 6b, and 6a. In the laser equipment constituted in this manner, part of laser beam 7 generated in the laser oscillator that is constituted by the totally reflecting mirror 1a, the partially transmitting mirror 2a, and the laser pumping sections 5a and 5b passes through the partially transmitting mirror 2a and is extracted, passes through the laser amplifier that is constituted by the laser pumping sections 5c and 50a, and then, after being amplified, is extracted as a laser beam 70.
The operation of the laser equipment according to the present embodiment is now described in detail. The
The
Parameters used for the calculations for
n(r)=n0−n2/2×r2
wherein n0=1.82, and n2 differs by the circumferential-direction polarization component (direction Φ) and by the radial-direction polarization component (direction r), and varies depending on the pumping energy density while maintaining the relationship n2r=n2Φ×1.2, n2 being approximately proportional to the pumping energy. For this reason, the direction Φ of n2 was decided so as to range from 0 to 0.8×10−4 (n2=0 at the leftmost point of the abscissa, n2=0.8×10−4 at the rightmost point in
It is understandable through comparison among
In the laser equipment constituted as illustrated in
In other words, in beam modes from a periodic constitution wherein equivalent constitutions with plane-curvature mirrors arranged in positions of equal distance from both ends of Nd:YAG rods are combined, the beam curvature in the two positions corresponding to the planar mirrors and to the intermediate point of the Nd:YAG rod is always planar. The positions corresponding to the plane-curvature mirrors are apart from the lenses, and are so-called condensing points whereat the beam diameter is small and the beam diameter significantly varies depending on the pumping intensity; in contrast, the positions corresponding to the intermediate points of the Nd:YAG rods are the emitting points from the lenses and are so-called collimating points whereat the beam diameter is large, and the variation in the beam diameter dependent on the pumping intensity is small. An output laser beam having small dependence on the pumping intensity can be obtained by extracting the beam from a collimating point in the periodic beam propagation. In contrast, in the conventional laser equipment described in
In the calculations represented in
It turns out from
The equipment constitution of the portion from which a beam is extracted and the variation in the beam diameter are described here in more detail with reference to
Here, in the embodiment illustrated in
In addition, although in the embodiment illustrated in
Moreover, in the case of the embodiment illustrated in
These also apply in each of the following embodiments, although they may not be especially described.
In the embodiment illustrated in
Moreover, in
Moreover, although in Embodiments 1 and 2, the laser active medium 40a is constituted in such a way that the excited region is half of the laser active media 4a, 4b, and 4c in length and has the same pumping energy density per unit length as the laser active media 4a, 4b; and 4c, the same effects as those in Embodiments 1 and 2 are demonstrated by making the length of the laser active medium 40a the same as that of the laser active medium 4a, and by exciting the laser active medium 40a by pumping energy half as dense as that of the laser active medium 4a. That is, the same effects as with Embodiments 1 and 2 are demonstrated by making the laser pumping energy of the laser pumping section in the position from which the laser beam 70 is extracted approximately half of the laser pumping energy of the other laser pumping sections, i.e., those located between adjacent beam waists.
Moreover, also cases where another pumping method and laser active media of other forms are used, if the thermal lens in the portion, through which the laser beam passes, of the laser active medium corresponding to 40a of Embodiment 1 is approximately half—i.e., if the thermal-lens focal length is approximately double—that of the thermal lenses in the portions, through which the laser beam passes, of laser active media corresponding to 4a, 4b, and 4c of Embodiment 1, the same effects as those of Embodiment 1 will be demonstrated.
In addition, in Embodiment 2, although it has been described that laser equipment wherein the variation in the beam wavefront curvature and beam diameter of the emitted beam 70 is very small can be obtained when the laser pumping energy of the laser pumping section that is the portion from which the laser beam 70 is extracted is approximately half of that of the other laser pumping sections, i.e., the ones located between adjacent beam waists, as described in Embodiment 1, the laser pumping energy is not limited to be approximately half; if the laser pumping energy of the laser pumping section that is the portion from which laser beam 70 is extracted is made smaller than that of the other laser pumping section (e.g., from 25% to 75%, preferably from 40% to 60%), laser equipment having an emitted beam in which the dependency of the beam wavefront curvature and beam diameter on the pumping energy is low can be obtained. Also in each of the following embodiments does this apply although this is not especially described.
Demonstrative experiment according to the present invention, which was carried out with laser equipment that utilized the side-LD-pumping type Nd: YAG rod laser and was constituted as shown in
In the laser pumping section 50a, 8 LDs 30a are arranged so as to form two rows along the beam-axis direction; in each row, 4 of the LDs 30a form 4-fold symmetry with respect to the rod-type solid-state laser active media 40a made of Nd YAG (the rod-type solid-state laser active medium 40a has a length of 70 mm, 36 mm of which is an excited portion, and a diameter of 4 mm) as a rotational-symmetry axis. The laser pumping section 50a is arranged constituting a laser amplifier on the beam axis outside the laser oscillator in such a way that the optical path length from the end face of the partially transmitting mirror 2a facing the laser pumping section 5b to an end face 120e of the rod-type solid-state laser active media 40a facing the partially transmitting mirror 2a is 400 mm.
With this constitution, the major portion of the laser beam 70, which passes through the laser pumping section 50a and is amplified therein, enters the power meter 26 after being reflected by the return mirror 25. Moreover, by monitoring leakage light that is not reflected by the return mirror 25, the position where wavefront curvature is infinite, the beam diameter in the position where wavefront curvature is infinite, and the quality of the beam were measured. By separately measuring the thermal lenses formed by the Nd: YAG rod-type solid-state laser active media 4a and 4b, the current values for the laser pumping sections 5a and 5b were set so that each of the thermal-lens focal lengths of the laser pumping sections 5a and 5b was identical. In addition, by separately measuring the thermal lens formed by the laser active medium 40a, the current value for the LDs 30a of the laser pumping section 50a was set in such a manner that the n2 value (refraction index: n(r)=n0−n2×r2/2) of the excited region of the thermal lens formed by the Nd: YAG rod-type solid-state laser active medium 40a was the same as the value for the thermal lens formed by the Nd:YAG-rod excited regions of the laser pumping sections 5a and 5b. Moreover, the measurement of the focal lengths of the thermal-lens formed by the Nd:YAG rod-type solid-state laser active media 4a, 4b and 40a was carried out by measuring the thermal-lens focal lengths when a collimated He—Ne laser beam was made to pass through the portion within a 1.5-mm circuit of the center of the Nd:YAG rod-type solid-state laser active media 4a, 4b and 40a, and varying the current value of the pumping LD.
In
In this situation, with the laser pumping section 50a installed, the position where the wavefront curvature is infinite approximately corresponds to the laser-emitting end of the solid-state laser active medium 40a of the laser pumping section 50a, and the position is the one where the laser beam is collimated. Moreover, as illustrated with black circles in
On the other hand, without the laser pumping section 50a installed, it turns out that the position where the wavefront curvature is infinite approximately corresponds to the position of partially transmitting mirror 2a, and is equivalent to a beam-waist position. Although the variation in the position is small as illustrated with the white circles in
It should be understood that effects close to those of the present embodiment may also be demonstrated by making the length of the excited region of the Nd:YAG rod-type solid-state laser active medium 40a of the laser pumping section 50a the same as the length of the excited region of the Nd YAG rod-type solid-state laser active media 4a and 4b of the laser pumping sections 5a and 5b. In that case, however, since the value of the LD driving current used for the pumping LDs 30a of the laser pumping section 50a needs to be below that of the LD driving current used for the pumping LDs 3a and 3b of the laser pumping sections 5a and 5b, there occurs inconvenience such as that with a single power supply a plurality of dc-coupled laser pumping sections cannot be driven, or that complicated current-regulation equipment is required.
A further problem is that if the Nd:YAG rod-type solid-state laser active medium 40a of the laser pumping section 50a is long, in order for a collimated beam to be extracted, n2 of the Nd: YAG rod-type solid-state laser active medium 40a needs to be made small by comparison to laser pumping sections 5a and 5b, and since beam-striking consequently occurs at the rim of the rod on the emitting end of the Nd:YAG rod-type solid-state laser active medium 40a of the laser pumping section 50a, efficient operation cannot be implemented.
What has been described above will be described in more detail. If fine corrections are ignored, the amount of energy extracted from the laser active medium is maximal when the definite integral of the product of the multiplication of the pumping intensity distribution in the excited region of the laser active medium by the intensity distribution of the beam which passes through the laser active medium, over the entire excited region of the laser active medium, is maximal.
In cascade-type laser equipment described in the present invention, in order to make extraction of energy maximal, in most cases the equipment is constituted so that the diameter of the propagation beam is as large as possible, as far as it does not exceed the effective diameter of the laser active media in the direction perpendicular to the beam axis, in the excited region of the laser active media in a plurality of laser pumping sections.
In such equipment, if n2 of the laser pumping section 50a is made smaller than those of the laser pumping sections 5a and 5b, since the diameter of the propagation beam within the laser active medium 50a will be larger than the diameter of those in laser pumping sections 5a and 5b and will exceed the effective diameter of the laser active media, beam-striking will occur in the rim of the rod, giving rise to a problem such as that the efficient operation cannot be implemented.
On the other hand, if the length of the excited region of the Nd YAG rod-type solid-state laser active medium 40a of the laser pumping section 50a is shorter than half of those of the Nd:YAG rod-type solid-state laser active media 4a and 4b of the laser pumping sections 5a and 5b, it is necessary to enlarge n2 of the Nd: YAG rod-type solid-state laser active medium 40a; and in order to extract a collimated beam, the beam diameter on the emitting end will be smaller. Accordingly, since energy cannot sufficiently be extracted from the excited region in the Nd:YAG rod-type solid-state laser active medium, the efficient operation cannot be implemented.
What has been described above will be described in more detail. If fine corrections, such as for the effects of diffraction, are ignored, the amount of energy extracted from the laser active medium is maximal when the definite integral of the product of the multiplication of the pumping intensity distribution in the excited region of the laser active medium by the intensity distribution of the beam which passes through the laser active medium, over the entire excited region of the laser active medium, is maximal.
In such equipment, if the beam diameter in the laser pumping section 50a is smaller than those of the laser pumping sections 5a and 5b, a region where the laser beam intensity is remarkably small is formed in the excited region of the laser active medium in the laser pumping section 50a; the efficient operation cannot be implemented since the definite integral of the product of the pumping intensity distribution in the excited region of the laser active medium and the beam-intensity distribution, over the entire excited region of the laser active medium, is smaller.
In consequence, when the excited-region length of the laser pumping section 50a is made half of those of the laser pumping sections 5a and 5b, the effects of the present invention are demonstrated more greatly.
Moreover, 111a is the reference mark indicating a position on the end face of the mirror 1b; 100a is the reference mark indicating an intermediate position in the laser active medium 4a; and 111b is the reference mark indicating a position where the sign of the beam-wavefront curvature in the lens changes.
In
Arranging in this way mirrors and lenses between laser active medium and laser active medium enables varying the beam diameter and the beam wavefront curvature of the laser beam in the laser active media in the same way as with the arrangement illustrated in
In addition, in
In addition, in
Moreover, 6a is the reference mark indicating an optical system between the positions 111a and 100a; and 6b is the reference mark indicating an optical system between the positions 100a and 111b. In the laser pumping sections 5a, 5b and 5c, optical components are arranged so that they implement a cascade-type constitution that repeatedly propagates a beam through the same optical system, i.e., so that they implement a periodic structure that is a thrice-recurrent 6a, 6b, 6a, 6b, 6a, 6b, with the combination of the optical systems 6a and 6b as a unit structure.
Moreover, the laser pumping section 50a is constituted in such a way that an optical system 6b is arranged between the position 100 and 111a so that in terms of optical properties, the position 100a of the optical system 6b corresponds to the position 100, i.e., so that a 6b, 6a, 6b, 6a, 6b, 6a, 6b structure is implemented when the overall constitution including the amplifier constituted by the laser pumping section 50a is indicated. In order to implement such a structure, as is the case with Embodiment 1, i.e., with the laser active medium 40a of the laser pumping section 50a arranged on the output end in
The laser amplifier constituted in this way, since the position 100 where a laser beam enters is the one equivalent to 100a where the pumping 15′ energy-dependent variation in the beam diameter and beam wavefront curvature is small, is constituted in such a way that an incident beam which maintains identicalness over the wide range of variation in the pumping energy of the laser active medium can be propagated without spoiling the cascade-like beam mode. In consequence, since the volume of the portion where the amplified beam mode and the excited region overlap is large, the efficient amplification can be implemented. Furthermore, since the incident beam which maintains identicalness over the wide range of variation in the pumping energy can be utilized, the design of an amplifier can be simplified.
In other words, in the beam mode from a periodic configuration in which constitutions wherein each of two plane-curvature mirrors is arranged at the same distance from either end of the rod-type laser active medium are equivalently combined, the beam curvature is always planar in two locations: the positions corresponding to the plane mirrors, and the intermediate point in the rod-type laser active medium. The positions corresponding to the plane mirrors are so-called condensing points which are away from the lens, and the beam diameter thereat is small; the beam diameter significantly varies depending on the pumping intensity. In contrast, the position corresponding to the intermediate point in the rod-type laser active medium is a so-called collimating point, which corresponds to the emitting point of the lens, and the beam diameter thereat is large; the variation in the beam diameter has small dependence on the pumping intensity. When a beam is made to enter this point, i.e., the collimating point in the periodic beam propagation, not being dependent on the pumping intensity the incident beam can be made to coincide with the propagation mode inside the cascade constitution, whereby highly efficient, stable inner-amplifier propagation without dependence on the pumping intensity can be obtained.
In addition, in Embodiment 5, although a case where the amplifier outputs from the position corresponding to 111b, as is the case with conventional laser equipment, has been described, it goes without saying that the variation in the output beam diameter and beam wavefront curvature in response to the pumping energy can be further diminished if a laser pumping section with half pumping energy, as illustrated in Embodiment 1, is arranged also on the output end. Moreover, in the present embodiment, four-stage-amplification constitution using four laser pumping sections is adopted for the laser amplifier but the constitution may be implemented with a different number of pumping sections for the amplifier, and as may be necessary, the laser equipment may be constituted by mirrors with curvature and lenses, as illustrated in Embodiment 4.
The operation of the laser equipment illustrated in
The subsequent laser equipment L2 has the same constitution as the laser equipment in
The operation of the laser equipment illustrated in
The subsequent laser equipment L2 has the same constitution as the laser equipment in
Furthermore, also by independently changing the pumping energy for the laser equipments L1 and L2, L1 and L2 can stably be combined over a wide range of pumping energy. In addition, even when the constitution of the laser active media and the laser active medium pumping devices for L1 is different from that of those for L2, L1 and L2—in each of their operative ranges—can be operatively combined. Moreover, damage resulting from excessively condensed beams on the end face of the optical fiber 16 can be averted. Furthermore, in
In
As described above, laser equipment may be constituted by dividing an pumping section equivalent to a single pumping section, such as 5a illustrated
In this case, the optical arrangement in the laser resonator differs from that illustrated in Embodiment 8, i.e.,
In addition, in Embodiment 9 also, the pumping energy of the laser pumping section 50a, which is in the beam-extraction-position end, is half of the sum of the pumping energy of the laser pumping sections 50d and 50e, which are situated between adjacent beam waists-between 111a and 111b.
According to Embodiment 9, laser equipment with mirrors arranged in the vicinity of the laser active media can be constituted. Moreover, the laser active media 40c and 40d can function respectively as a totally reflecting mirror and as a partially transmitting mirror when they are coated on their end faces. Moreover, in the laser equipment constituted as in
In laser equipment constituted as that in
The constitution of the laser equipment according to Embodiment 11 is now described in detail. In
In other words, the optical path length from the totally reflecting mirror 1a to the end face of the solid-state laser active medium 41a, and the optical path length from the partially transmitting mirror 2a to the end face of the solid-state laser active medium 41b, are each half of the optical path length from the end face of the solid-state laser active medium 41a to the end face of the solid-state laser active medium 41b. On the other hand, the solid-state laser active medium 41c is constituted in such a manner that the length from the end face of the solid-state laser active medium 41c to the end face of the partially transmitting mirror 2a is equal to the length from the end face of the solid-state laser active medium 41b to the end face of the partially transmitting mirror 2a.
In addition in
The operation of laser equipment according to the present embodiment is set forth below. The laser oscillator constituted from the totally reflecting mirror 1a, the solid-state laser active media 41a and 41b, and the partially transmitting mirror 2a, with both end faces of the solid-state laser active media 41a and 41b being excited by the laser active medium pumping devices 31a, 31b, 31c and 31d, generates a resonator internal laser beam 7. The solid-state laser active medium 41c arranged on the beam axis functions as a laser amplifier by being excited by the laser active medium pumping device 31e. The laser beam 7 is extracted through the partially transmitting mirror 2a to the outside of the resonator and amplified while passing through the solid-state laser active medium 41c, and then is extracted as the laser beam 70 to the outside of the laser oscillator and the laser amplifier.
In the laser oscillator and the laser amplifier constituted in this manner, since the emitting-side end face of the solid-state laser active medium 41c is not excited, the thermal-lens focal length of the solid-state laser active medium 41c is longer than those of the other laser active media 41a and 41b, and the variation, depending on the pumping intensity, in the beam diameter and in the beam curvature of the laser equipment can be diminished. Moreover, when the pumping power absorbed from the laser active medium pumping device 31e by the solid-state laser active medium, and the pumping power absorbed from the laser active medium pumping devices 31a, 31b, 31c and 31d by the solid-state laser active media, are identical, the present invention demonstrates its greatest effect. In that case, since the beam is extracted from the collimating point, which is not dependent on the pumping intensity, in the periodic beam propagation, a beam that is approximately collimated can be extracted without being dependent on the pumping intensity.
As described heretofore, in each of Embodiments 1 through 11, a plurality of laser pumping sections is arranged in a cascade and constituted in such a manner that beam waists are periodically generated by the thermal lenses of the laser active media, and the incident end or the emitting end is situated in the position where the beam diameter of the laser beam is maximal, by setting the pumping energy of the laser pumping section that is arranged beyond the beam waist situated in the endmost incident or emitting position to half of the sum of the pumping energy of the pumping sections located between adjacent beam waists. As a result, laser equipment can be provided that can obtain an output beam with small pumping energy-dependent variation in the beam diameter and in the beam wavefront curvature; or an amplifier can be provided that can propagate an incident beam that remains identical over a wide range of pumping energy without deforming the cascade-type beam mode.
In the laser equipment constituted in the foregoing way, since laser equipment according to the present invention described in any one of Embodiments 1 through 11 is utilized as a fundamental-wave beam source, pumping energy-dependent variation in beam diameter and in wavefront curvature of the emitted beam from the laser beam source 11 is slight. Accordingly, laser equipment having high conversion efficiency over a wide range of pumping energy, i.e., a wide range of output power, can be provided. Moreover, since the beam wavefront curvature and beam diameter of the wavelength-converted laser beam vary depending on variation in the beam wavefront curvature and beam diameter of the fundamental-wave beam in the position of the wavelength-conversion active medium, a beam source for a wavelength-converted laser beam can be provided, wherein variation in the beam diameter and beam wavefront curvature of the wavelength-converted laser beam with respect to change in pumping energy of the laser equipment 11 is slight.
In addition, in the present embodiment, although the constitution is implemented in such a manner that a desired wavelength-converted laser beam is generated through a single wavelength-conversion stage, as may be necessary, the wavelength conversion may be carried out with two or more types of wavelength-conversion devices, or two or more devices configured on the beam path.
The operation of the laser equipment illustrated in
In a laser machining device constituted as that in
Laser equipment according to the present invention can be utilized, for example, as a laser machining device, and since such a laser machining device can perform very precise, consistent work with long-term stability, it can advantageously be used, e.g., in various processes such as manufacturing printed circuit boards and fiber gratings. Moreover, in the laser equipment according to the present invention, since pumping intensity-dependent variation in output-beam diameter is small, the effects are largely demonstrated especially in the application in which a laser beam is utilized in a condensed state; for example, welding-purpose lasers or cutting-purpose lasers that utilize optical-fiber beam guidance associated with beam condensation, or wavelength-converted lasers associated with beam condensation. In these applications, since stable processing characteristics can be obtained without depending on the pumping intensity, the operation is easy, and inconsistencies in characteristics caused by inconsistencies in components used in identical tool types can be suppressed.
Kojima, Tetsuo, Fujikawa, Shuichi, Konno, Susumu
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